On 07/29/15 13:09, Luis R. Rodriguez wrote:
> From: "Luis R. Rodriguez" <[email protected]>
>
> Recursive dependency issues with kconfig are unavoidable due to
> some limitations with kconfig, since these issues are recurring
> provide a hint to the user how they can resolve these dependency
> issues and also document why such limitation exists.
>
> Cc: Geert Uytterhoeven <[email protected]>
> Cc: James Bottomley <[email protected]>
> Cc: Josh Triplett <[email protected]>
> Cc: Paul Bolle <[email protected]>
> Cc: Herbert Xu <[email protected]>
> Cc: Takashi Iwai <[email protected]>
> Cc: "Yann E. MORIN" <[email protected]>
> Cc: Michal Marek <[email protected]>
> Cc: Jonathan Corbet <[email protected]>
> Cc: [email protected]
> Cc: [email protected]
> Cc: [email protected]
> Signed-off-by: Luis R. Rodriguez <[email protected]>
> ---
>
> I've cc'd Roberto and Stefano as I think we might be able to in the
> long term use some of their work on package dependency and solvers for
> this problem [0] [1] [2]. This last part -- just consider it long term
> focused.
>
> [0] https://upsilon.cc/~zack/research/publications/splc2010-fd-deps.pdf
> [1] https://ocaml.org/meetings/ocaml/2014/preferences-2014-09-05-slides.pdf
> [2] https://www.youtube.com/watch?v=GSOcRQvZg8w
>
> Documentation/kbuild/kconfig-language.txt | 22 ++++++++++++++++++++++
> scripts/kconfig/symbol.c | 2 ++
> 2 files changed, 24 insertions(+)
>
> diff --git a/Documentation/kbuild/kconfig-language.txt
> b/Documentation/kbuild/kconfig-language.txt
> index 350f733bf2c7..7e0510d1cef7 100644
> --- a/Documentation/kbuild/kconfig-language.txt
> +++ b/Documentation/kbuild/kconfig-language.txt
> @@ -393,3 +393,25 @@ config FOO
> depends on BAR && m
>
> limits FOO to module (=m) or disabled (=n).
> +
> +Kconfig recursive dependency limitations
> +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> +
> +If you've hit the Kconfig error: "recursive dependency detected" you've run
> +into a recursive dependency issue with Kconfig. Kconfig does not do recursive
> +dependency resolution, this has a few implications for Kconfig file writers.
> In
maybe s/,/;/
> +practice it means that for instance if a driver A selects a few kconfig
> symbols
> +another driver B which selects any of these symbols cannot negate any of the
> +symbols the driver A selected. Because of this current limitation developers
> +who run into this type of recursive dependency issue have two diverging
> +options:
> +
> + a) Either swap all "select FOO" to "depends on FOO" or,
> + b) Change the offending "depends on FOO" to "select FOO"
> +
> +Kconfig's limitations can be addressed by implementing a SAT solver for it,
> +but until then, Kconfig is limitted to require developers to use one of
limited
> +the above two mechanisms to address recursive dependency issues. For more
> +details you can refer to this thread and discussion:
> +
> +http://lkml.kernel.org/r/[email protected]
--
~Randy
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